I've used these thing for years.....
First off.... They are designed oversize, so they can be hand fit to a variety of shock bodies. No problem there, just be aware of it before buying. Of course you need to have good attention to detail to sand them to the same size.... Very important.
They only work well in certain situations. If the track is smooth, high bite, I don't like them. Even with low bite, if the track is freshly groomed, and not very bumpy, I stay away.
When they really seem to shine is bumpy, rutty tracks. The faster rebound lets the wheels drop down between bumps to keep some contact with the surface. On tracks that have deteriorated a bit they work quite well. Some tracks that develop nasty bumps and ripples in the braking and acceleration zones are where you really want to try these. If you race at a track that runs 1/8 scale as well as 1/10, and the track goes to hell as the day progresses, these may very well save you at the end of the day.
Since I only really use them when traction is low, I've only really used the light ones. If you speak Associated
...... I offer this:
The blue pistons are a little less pack than #2's, the whites are a little less pack than #1's.